Quantitative measures of the distal finger and nail can be used to quantitatively assess a person for finger clubbing. Although there are inherent differences in curvature between the fingers, clubbing appears to advance uniformly in all digits and in both hands.

Different parameters that can be measured:

(1) profile angle (angle of line tangent to the surface of the proximal fingernail)

(2) hyponychial angle (angle of line drawn to hyponychia from cuticle)

(3) curvature of nail in diopters

Techniques used to observe the finger:

(1) finger cast in plaster of Paris

(2) shadowgraph (uses an magnifying lens over a lightbox)

(3) projection onto a screen using an overhead projector

Observations:

(1) Although clubbing may be measured on any digit, comparison between individuals must be made using the same finger(s).

(2) Accuracy in measurement and calculations is important.

(3) Measurements for an individual over time may be more useful than a single determination. This allows trends to be observe, such as worsening of the underlying condition.

(4) The hyponychial angle seems to be the best discriminator for finger clubbing.

Profile Angle

Technique:

(1) An imaginary line is drawn from the distal digital crease (between distal phalanx and middle phalanx) and the cuticle (line DC).

(2) The distance from the cuticle to the fingertip is measured.

(3) At a point one third the distance from the cuticle to the fingertip, the profile of the nail is indicated as point P.

(4) An imaginary line is drawn from the cuticle to point P (line CP).

(5) The profile angle is the angle going clockwise through the cuticle from line DC to line CP.

(6) The profile angle used by Bentley et al seems slightly different, in that the distance along the cuticle to hyponychia is used for reference rather than the distance to the finger tip. In addition, a line is drawn at right angles from the cuticle-hyponychial line to the outer surface of the nail to determine the point for measuring the profile angle. This alters the profile angle a few degrees from that of Regan et al.

Since the profile angle is usually < 180°, it can be measured as 180° minus the angle alpha (as follows):

tan (alpha) =

= (distance of point P above extended line DC) / (length of one third the distance from the cuticle to the fingertip)

Profile angle interpretation by Regan et al:

(1) mean clubbed: 181.1 degrees

(2) mean normal: 173.5 degrees

(3) midpoint between 177.3 degrees

According to Sinniah and Omar, using the method of Bentley et al, the profile angle showed the following:

(1) normal controls: 154-176 degrees (mean 171.4 +/- 5.5 SD)

(2) patients with clubbing: 171-189 degrees (mean 182.9 +/- 4.7 SD)

Hyponychial Angle

Technique:

(1) An imaginary line is drawn from the distal digital crease (between distal phalynx and middle phalynx) and the cuticle (line DC).

(2) An imaginary line is drawn from the cuticle to the hyponychia (line CH).

(3) The hyponychial angle is the angle going clockwise through the cuticle from line DC to line CH.

Since this is usually > 180°, it can be measured as 180° plus the angle beta (as follows):

sin (beta) =

= (distance of hyponychia below extended line DC) / (length of line CH)

Profile angle interpretation by Regan et al:

(1) mean clubbed: 209.4 degrees

(2) mean normal: 187 degrees

(3) midpoint between: 198.2 degrees

According to Sinniah and Omar, using the method of Bentley et al, the hyponychial angle showed the following:

(1) normal controls: 165-189 degrees (mean 180.7 +/- 5.2 SD)

(2) patients with clubbing: 178-205 degrees (mean 194.5 +/- 7.5 SD)

Curvature of Nail in Diopters

The curvature of the nail can be measured in diopters with a spherometer used to measure lenses. According to Regan et al, the curvature differs between the different fingers with the thumb the least curved and the index finger the most.

Digit |
mean of normal fingers |
midpoint |
mean of doubtful fingers |
midpoint |
mean of clubbed fingers |

1 (thumb) |
4.5 |
5.75 |
7 |
9.5 |
12 |

2 (index) |
9.5 |
11.25 |
13 |
15 |
17 |

3 (middle) |
8.5 |
9.5 |
11.5 |
13.25 |
15 |

4 (ring) |
7.5 |
8.75 |
10 |
12 |
13 |

5 (little) |
9 |
10.75 |
12.5 |
14.25 |
16 |

from Figure 3, page 531, Regan et al

**Specialty: **Pulmonology

**ICD-10: **,